As manufacture process rules of semiconductor products become more rigorous for higher IC integration, inclusion of trace impurities largely affects on device performance and product yield of the semiconductor products. To prevent inclusion of trace impurities, rigorous contamination control has been required and a variety of cleaning is performed in each process in manufacture processes of semiconductor products.
Generally, as a semiconductor substrate (silicon wafer) cleaning liquid to be used in FEOL before forming a wiring pattern, a mixture of ammonia water, hydrogen peroxide water and water (SC-1) for the purpose of removing fine particles, a mixture of hydrochlonic acid, hydrogen peroxide water and water (SC-2) for the purpose of removing metals, dilute hydrofluoric acid, ozone water, a mixture of ozone water and dilute hydrofluoric acid, a mixture of sulfuric acid and hydrogen peroxide water (SPM) for the purpose of removing organic substances, and a mixture of sulfuric acid, ozone and water, etc. are used. They are used alone or in combination in accordance with the purposes.
In a conventional cleaning process (an RCA cleaning method and an improved cleaning methods thereof), after treating substrate surfaces with a cleaning liquid as above, a rinsing process for rinsing the substrates with ultrapure water for washing the cleaning liquid away is performed inevitably. At this time, if any contaminant even in a slight amount is in the ultrapure water, the contaminant adheres to the substrate surfaces, so that demands for purity of the ultrapure water for rinsing have been very high.
However, demands for purity of ultrapure water for rinsing in recent years are liable to be too high disregarding costs and conveniences for fear of causing adhesion of contaminants to substrate surfaces. Particularly, in the case of metals which become a problem of contaminants, since it is safer to lower a concentration of trace metals in the ultrapure water, the current situation is to just focus on lowering the entire concentration without verifying the effects that what components should be decreased to what level.
When using ultrapure water as a rinsing liquid, a high specific resistance value of ultrapure water results in problems, such that static generates in the rinsing treatment to cause an electrostatic breakdown or dirt adheres to cleaned substrate surfaces due to the static. To solve the problems, a technique of dissolving ammonia in the ultrapure water is disclosed in the patent article 1.
On the other hand, the patent article 2 discloses a cleaning method of removing metal impurities adhered to substrate surfaces by bringing cleaning subjects contact with a cleaning liquid obtained by dissolving an ozone gas and carbon dioxide in pure water or ultrapure water.
Furthermore, the patent article 3 describes that, when rinsing substrates having metal wirings formed thereon by using ultrapure water, ultrapure water containing a chelate agent is used as a rinsing liquid so as to prevent metal adhesion as well as re-adhesion of metals, once dissolved from the metal wirings on the substrate surfaces due to the ultrapure water, to the substrates.